The invention relates to a radial-piston pump, in particular a high-pressure gasoline pump. The radial-piston pump has at least one delivery unit and a separating device that separates a first accommodation space for a medium to be delivered and a second accommodation space for a lubricant from one another. A sealing element is provided on a casing side and a further sealing element is provided on an eccentric side that is fluid-tightly connected to the sealing element.
Radial-piston pumps of this kind, which are known, for example, from DE 43 05 791 A1, are used as fuel pumps for internal combustion engines. Fuel is delivered by means of at least one radial piston, which is actuated by an eccentric of a shaft. It is customary for three such radial pistons to be distributed uniformly around the outer circumference of the eccentric shaft. Each of the radial pistons rests via a sliding shoe and an eccentric ring on the eccentric shaft. The eccentric ring is supported rotatably on the eccentric shaft via a sliding-contact bearing and ensures reliable guidance of the sliding shoe with minimum frictional losses. The cylinders for accommodating the radial pistons are arranged in the pump casing and are each provided with an intake valve and a delivery valve, via which the fuel can be drawn in from the crank space and via which the pressurized fuel can be passed to the internal combustion engine.
The known radial-piston pump is lubricated by means of a separate lubricant circuit in which the lubricant is passed to the shaft bearings and the sliding-contact bearing of the eccentric ring through an axial hole in the eccentric shaft.
In pumps of this kind, there is a constant need to ensure that the lubricant circuit is sealed off from the fuel circuit, in particular from the crank space of the eccentric, thus eliminating the possibility of leakage flow, which would impair either the efficiency of the pump or have a negative effect on lubrication.
In the known pump, this is prevented by a comparatively complex construction with spring-loaded thrust washers which, on the one hand, are used for axial guidance of the eccentric ring and, on the other hand, act on seals which separate the crank space from the lubricant circuit.
For delivery of volatile fuels such as gasoline, special measures are required to suppress the formation of vapor bubbles over the entire speed and temperature range of the engine. Since the fuels generally have a lower viscosity than diesel, relatively small component tolerances are required, especially in the sealing region, to prevent leakage flows. However, such small component tolerances necessitate a considerable outlay in terms of manufacture and this increases the production costs for the pump.
DE-A 197 01 392 discloses a radial-piston pump in which a cam is situated on the input shaft in an approximately central position in a space which is separated by an axially arranged separating element into a working-fluid zone and a lubricant zone. Since the flexible separating element is therefore very long in the axial direction, the outlay in terms of manufacture is likewise high in the case of this radial-piston pump.
International application WO 95/33924 relates to a piston pump in which a lubricant space provided at the circumference of the eccentric and a lubricant space in the vicinity of the input-shaft bearing portion are connected by a lubricant passage in the input shaft. In this piston pump, the outlay on equipment required to seal off the lubricant spaces is high by its very arrangement.
DE-A 196 37 646 discloses a radial-piston pump in a hydropump unit, in which pump a rod-shaped eccentric element is mounted eccentrically in the input shaft at one end and in a manner fixed relative to the casing at the other end, with the result that it moves within the envelope surface of a cone as the input shaft rotates. The bearing portions on the rod-shaped eccentric element are not lubricated reliably and independently of the working-fluid circuit.
Given this situation, the object on which the invention is based is to provide a radial-piston pump in which leakage flows can be reduced with a minimum outlay in terms of equipment.